There is widespread use of various metal tubing arrangements used to convey electrical or optical conductors to various measurement instruments installed in sealed housings. These sealed housings are often placed in extreme environments as for example, in wellbores used for oil and gas exploration.
There is a growing trend to use double wall concentric tubing in such applications, so that the outer tube provides a primary barrier against entry of fluids. The inner tubing that encapsulates electrical or optical conductors provides a secondary barrier in case of rupture of the outer tube.
Especially in the case of concentric tubes, when the outer tube is ruptured, high pressure well fluids can enter the cavity (annulus) around the inner tube and potentially contaminate instruments inside the instrument housings connected to the inner tube. So the annulus between the concentric tubes must be properly sealed from the instrument housing to prevent such contamination.
Because of the critical nature and cost of such systems, the industries that use them desire the ability of field-testing critical external seals that prevent the entry of wellbore fluids that would contaminate and disable such systems.
U.S. Pat. Nos. 7,219,736; 7,784,838; 8,037,933; 8,176,612; and 8,186,202 are prior art examples of systems which allow some testing of critical seals. These examples are based on simple tube connectors (“unions”), which provide for testing of primary seals against the outside diameter of the tubes. This approach will be explained further in the Detailed Description section. But the existing art does not provide testable connection of concentric, double-wall tubes, including annular seal, to hermetically sealed housings.
There is a need then for a field testable connection of such concentric, double-wall tubes, including annular seal, to hermetically sealed housings. The meeting of this need will be described.